Electrochemical techniques are recognized as very important candidates for the development of biosensors to be used in non-specialized environments. Although there has been intensive research into amperometric biosensors and some of them have successfully reached the commercialization stage, there have been few reports of the use of biomolecules in potentiometric sensors except for the use of antibodies for the detection of bacteria, viruses and marker proteins via potentiometric principles.
De Wael et al. in Analytical Chemistry (2012) 84:4921-4927, reported the first use of potentiometric sensors to study molecular interactions in liquid environments with sensorgram methodology.
Aptamers have shown enormous potential in selectively detecting drugs, toxins, proteins etc. Sassolas et al., Electroanalysis 21(11) (2009) 1237-1250 reported the use of aptamers as the bio-recognition element in potentiometic sensors. When combined with Ion Sensitive Field Effect Transistors (ISFETS) as readout systems in poten-tiometric sensors, aptamers appear better than antibodies, due to their smaller size.
Pilehvar et al. in Anal. Chem. (2012) 84:6753-6758, reported a novel, label-free folding induced aptamer-based electrochemical biosensor for the detection of chloramphenicol (CAP) in the presence of its analogues.
Despite the fact that aptamers are chemically more stable than proteins, they have to be protected from nucleases. Moreover, in respect of electrochemical biosensors, the electrode surface also needs to be protected from unspecific adsorption and oxidation/reduction reactions occurring while analyzing real samples.
WO 2005/103664 discloses composite potentiometric electrodes for selective analyte detection in a sample comprising a sensing body made from a polymeric material, preferably plastified polyvinyl chloride, comprising:                electrically conducting particles, preferably graphite powder, which increase in concentration away from a sample contact surface,        ionophore molecules, which increase in concentration towards the sample contact surface, and        an electrical connection, preferably made of copper, which passes proximal to said electrically conducting particles.        
Selecting an appropriate host matrix for aptamers is one of the main challenges for the immobilization of aptamers in order to improve the analytical characteristics of aptasensors. There is also a need for more sensitive and more specific potentiometric sensors, in particular electrodes, to study molecular interactions in liquid environments with a sensorgram methodology.